A. Field of the Invention
This invention relates generally to systems that provide mobile Internet Protocol (IP) networking, wherein a mobile communications device such as a portable laptop computer or personal digital assistant may communicate with a host computer on an IP network. More particularly, the invention relates to the architecture and arrangement of communications devices functioning as home agents and foreign agents that are used in such a system.
B. Description of Related Art
Public packet switched networks can be used to carry traffic to and from a mobile communications device, such as a laptop computer or personal digital assistant equipped with a cellular telephone modem. The basic architecture of mobile IP data networking is known in the art and described in several publications, including the Request for Comments document RFC 2002 (1996) and in the textbook of Charles E. Perkins, Mobile IP Design Principles and Practices, Addison-Wesley Wireless Communications Series (1998), both of which are fully incorporated by reference herein. Persons skilled in the art of mobile IP data networking are familiar with the contents of both of these documents and the devices used to implement mobile IP data networking in practice.
Basically, and with reference to FIG. 1, in Mobile IP communication, a wireless mobile node 10 communicates with a target host 12 on an IP network 14 by means of two devices, a “foreign agent” 16 and a “home agent” 18. Typically, foreign agent functionality is incorporated into a router or network access server chassis located on a mobile node's visited network 20. A radio access network linking the mobile node to the foreign agent 16 is not shown for purposes of simplicity in the present discussion. The foreign agent 16 provides routing services for the mobile node while it is registered with the home agent 18. The foreign agent 16 de-tunnels and delivers datagrams to the mobile node 10 that were tunneled by the mobile node's home agent 18. In the present specification, the term “tunneling” refers to packet re-addressing, such as performed by the home agent.
The traffic exchanged between the foreign agent 16 and the home agent 18 includes control traffic 22, e.g., registration request and registration reply messages and session control messages, and data traffic 24. The control traffic 22 terminates at the home agent. The data traffic 24 is routed from the mobile node's home network 26 to a second network 14 for delivery to the target host. The target host could be connected to the home network by any arbitrary number of intermediate IP networks, or could be on the mobile node's home network 26.
The home agent 18 is typically implemented in a router on a mobile node's home network 26. The home agent maintains current location information for the mobile node, through a variety of possible mechanisms, such as described in the patent application of Richard J. Dynarski, et al., “Dynamic Allocation of Wireless Mobile Nodes Over an Internet Protocol (IP) Network”, Ser. No. 09/233,381, which is incorporated by reference herein. When one or more home agents are handling calls for multiple mobile nodes simultaneously, the home agent(s) are providing, in essence, a service analogous to virtual private network services. Each mobile node is typically associated with a separate home network and the routing path from that home network, through the home agent, to the foreign agent and mobile node is like a virtual private network for the mobile node.
Thus, from the above discussion, it can be seen that the home agent performs two separate and distinct tasks for the foreign agent and mobile node. First, the home agent 18 must perform an authentication and registration process to determine whether the mobile node is authorized to access the home network 26. This may involve checking the identification of the mobile node (such as, through use of the mobile node's unique serial number or manufacturing number), password authentication, and possibly checking that the mobile node's account is current and paid in full. The home agent registration and authentication functions may be performed in conjunction with, or with the assistance of, a second device, such as an authentication, authorization and accounting server such as a RADIUS server. See the patent application of Yingchun Xu, Ser. No. 08/887,313 filed Jul. 3, 1997 for further details.
Second, the home agent 18 has to tunnel data from the target host to the foreign agent, and provide tunneling services in the reverse direction, i.e., provide packet re-addressing for traffic from the foreign agent to the host 12. To coordinate tunneling in the reverse direction, the home agent provides a forwarding “care/of” address to the foreign agent to tell the foreign agent 16 where to tunnel traffic from the mobile node so that it can be sent to the host. This forwarding address is typically contained in a registration reply message sent to the foreign agent notifying the foreign agent that the mobile node is authenticated to communicate in the home network. In the prior art, the home agent is also the device that receives the tunneled traffic from the foreign agent for routing onto the home network, and therefore the forwarding address is the home agent's IP address.
The foreign agent also has to perform two distinct tasks for the mobile node, similar to that of the home agent. First, the foreign agent has to handle the registration and session control aspects for the mobile node, including sending registration request messages to the home agent and processing a registration reply message. Second, the foreign agent has tunneling responsibilities for forwarding data packets to the home agent for ultimate distribution to the destination, and de-tunneling data from the home agent and forwarding the data to the mobile node.
The known prior art for providing mobile IP networking services has embraced the concept of a single home agent, in a single chassis, for a given network. However, some larger scale providers of Mobile IP networking services may require multiple home agents on their networks in order to meet demand for mobile IP network services for a large distributed customer base. One possible approach to meeting the expected demand for home agent services is to provide multiple home agents, each home agent embodied in a separate chassis or device. Another approach is to provide a single home agent, but design the home agent such that it has an internal architecture to support multiple networks (e.g., multiple virtual private networks). This latter approach is not considered very attractive, in that management of the home agent would be cumbersome. Furthermore, the home agent would not be particularly fault tolerant, in that any mechanical or software problem in the home agent would potentially affect a large number of virtual private networks. In all the known prior art, the individual devices configured as home agents have implemented both home agent functions within the same device, i.e., registration functions and tunneling/routing functions as described above. Similarly the prior art has embraced the concept of performing both the registration and tunneling responsibilities for a foreign agent in a single device, e.g., network access server.